1. Field of the Invention
One embodiment of the present invention relates to a display device.
The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. One embodiment of the present invention relates to a semiconductor device, a light-emitting device, a power storage device, a memory device, a driving method thereof, or a manufacturing method thereof. In particular, one embodiment of the present invention relates to a semiconductor device, a display device, or a light-emitting device each including an oxide semiconductor.
In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. In some cases, a display device, an electro-optical device, a semiconductor circuit, or an electronic device includes a semiconductor device.
2. Description of the Related Art
Specific structures of active-matrix display devices using light-emitting elements differ depending on manufacturers. In general, at least a light-emitting element, a transistor (switching transistor) which controls input of a video signal to a pixel, and a transistor (driving transistor) which controls the amount of current supplied to the light-emitting element are provided in each pixel.
When all the transistors in the pixels have the same polarity, it is possible to omit some of steps for manufacturing the transistors, e.g., a step of adding an impurity element imparting one conductivity type to a semiconductor film. Patent Document 1 discloses a light-emitting element type display in which transistors included in pixels are all n-channel transistors.
In an active-matrix display device including light-emitting elements, variation in threshold voltage among transistors for controlling the amount of current supplied to the light-emitting elements in accordance with image signals (such transistors are also referred to as driving transistors) is likely to influence the luminances of the light-emitting elements. Patent Document 2 discloses a circuit configuration for preventing the above-described variation in threshold voltage from influencing the luminances of the light-emitting elements.